1. Field of the Invention
The present invention relates to a fuel tank made of resin mounted on an automobile and the like.
2. Description of the Related Art
In a fuel tank mounted on an automobile a tank made of resin by a blow molding in these years becomes a main flow from a viewpoint such as anti-rust and weight saving. Usually, to the fuel tank are attached various components such as a vent valve for leading out a fuel-vapor gas in a space over a liquid surface out of the tank and keeping a tank inside pressure constant, a check valve connected to a filler tube, and a fuel pump; and in a case of a fuel tank made of resin it is desirable that the components are connected with a tank main body by a thermal deposition from a viewpoint of a simplification of a manufacturing process.
FIG. 4 is a partial section drawing showing an attachment structure of a component in a conventional fuel tank made of resin. A symbol 24 shows a tank main body of the fuel tank made of resin, a component 31 is attached to a through hole drilled in a housing wall of the tank main body 24. In FIG. 4 the component 31 is shown as a check valve and is equipped with a joint portion 32 having a flange 36 connected with an outer surface of the tank main body 24, and a tubular valve main body portion 33 provided with a valve mechanism 40 at a top end thereof. Upon forming a primary molding portion 37 formed of a material, which can be deposited, on the tank main body 24 and a hole 39 where a melting resin material is passable, the joint portion 32 has a secondary molding portion 38 consisting of an HC (hydrocarbon) barrier material layer formed by a two-color molding method on a part of an inner periphery of the flange 36. An HC barrier material is generally a non deposition member.
On the other hand, a housing of the valve main body portion 33 is formed of the non deposition member such as POM (Polyoxymethylene, polyacetal resin). The valve main body portion 33 is engaged in the joint portion 32, and an O-ring 52 is provided at a part of an engagement face thereof. The O-ring 52 is something for ensuring air tightness between inside and outside of the tank. Usually, in a fuel tank is provided a breather opening (not shown) as an air breather in filling oil, and it is designed that an air breathing within the fuel tank is basically performed only through the breather opening. Accordingly, if a gap exists between the joint portion 32 and the valve main body portion 33, there is a possibility of an air leak from the gap; the O-ring 52 is something provided for preventing the air leak.
Now then, because in the component 31 an outside of the flange 36 is formed as the primary molding portion 37, the outside of the flange 36 is connected with the tank main body 24 by a thermal deposition at an outer wall side of the tank main body 24. Because an inside portion of the flange 36 fronting an inside of the tank main body 24 is formed of the secondary molding portion 38 consisting of the HC barrier layer, a permeation of HC (hydrocarbon) to an outside of the tank is suppressed by the secondary molding portion 38. The structure thus described is disclosed, for example, in FIG. 1 and paragraph [0022] of Japanese Patent Laid-Open Publication No. 2003-2074.
Because in the conventional component 31 connection portions with the joint portion 32 and the valve main body portion 33 are formed by a non deposition member, respectively, these cannot be connected by a thermal deposition, and therefore, the structure is designed so that a gap between the both is sealed by the O-ring 52, upon engaging the valve main body portion 33 in the joint portion 32 as described above. However, the structure of making the O-ring 52 intervene results in causing an increase of a component number and a lowering of a build efficiency.
Consequently is strongly requested an attachment structure of a fuel tank made of resin for improving a seal property and satisfying strength, rigidity, and a high barrier property without making a seal member such as an O-ring intervene.